Page 22 - Oceans

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Midocean ridges

plates of the earth's
Ocean floor is formed where plates of oceanic crust move crust move apart
Ridge pushed
apart to create a spreading rift. This relieves pressure on the up by heat
hot mantle rock below, and since pressure is all that keeps Rift valley forms
as crust sinks
the hot rock solid, it turns into molten magma and squirts Heated water
erupts at rift
up through the rift as basalt lava. The lava cools in the Molten basalt
cold ocean waters to form the solid rock of the ocean floor. ≤ spreading rift erupts at rift

Meanwhile, the magma chamber beneath the rift makes the Where the ocean floor is being pulled apart by convection
currents in the hot mantle below, big blocks of oceanic crust
rock expand, raising the crust on each side of the rift into two sink to form a rift valley at the boundary. The floor of the valley
is full of fissures, which erupt basalt lava and superheated water
lines of submarine mountains that form a midocean ridge. rich in dissolved chemicals. On each side of the rift, blocks of
ocean crust are raised into ridges by the heat, but they gradually
sink again as they slowly move away from the hot zone.

< Winding ridges
The midocean ridges created by rifting
and uplift extend for vast distances across the
ocean floor. The Mid-Atlantic Ridge—seen here
on the Heezen–Tharp map—extends for about
10,000 miles (16,000 km), all the way from rifts
the Southern Ocean to the Arctic Ocean. Its
mountains are up to 13,000 ft (4,000 m) high,
but their peaks lie 6,500 ft (2,000 m) beneath
the surface of the ocean.

Earthquake zone
< transform faults
Transform Rift offset by Midocean ridges are split
fault transform fault into short sections divided by
long transform faults that cut
straight across them. These
faults are very obvious features
of the ocean floor map shown
on the far left. They are caused
by slightly different spreading
rates along the rift. Where they
link sections of the spreading
rift, the ocean floor on either
Magma
rising beneath side of the fault is moving in
spreading rift opposite directions, and this
causes submarine earthquakes.
Movement of
oceanic plate

< the opening atlantic
The winding route of the
Mid-Atlantic Ridge echoes
the shapes of South America
and Africa. This is not a
coincidence. Some 130
million years ago the two
continents were joined
together, but then a rift
opened up between them,
as seen here. The rift was
flooded with water, and
a new ocean floor formed
in the widening gap to
create the Atlantic Ocean.